1. Field of Invention
The present invention relates to a method for detecting a parfocality of a stereo microscope, and more particularly to a method for detecting a parfocality of a zoom-stereo microscope.
2. Description of Related Arts
Stereo microscopes play a more and more important and valuable role in contemporary world industry. The stereo microscope is capable of observing a stereo image of an object, to further realize functions of stereoscopic measurement, automatic operation, three-dimensional reconstruction, etc. Especially in stereoscopic microoperation, precision control can be realized by sending instructions to manipulators, wherein the instructions are acquired via high resolution stereoscopic microscopic image processing. A zoom-stereo microscope is able to provide images which are always clear at different magnifications, to customers, therefore a requirement for the zoom-stereo microscope is also getting more and more. For a microscope, at a certain magnification, if a clear target image is obtained via adjustment, the position of the objective lens at the moment is called a parfocal position. If the clear target image can not be obtained via adjustment, the parfocal position doesn't exist. For a zoom lens set, if the clear target image can be obtained via adjustment at a high magnification, the target image should keep clear in a course of zooming to a low magnification, which is called parfocality. However, in delivery of the zoom lens sets, one or more lenses may shift due to vibration, etc., which causes a decrement of the parfocality. It means that the target image can not keep clear in the course of zooming to a low magnification from a high magnification, even at some magnification, the focal distance is required to be adjusted to obtain the clear target image, even worse, the clear target image can not be obtained via adjusting the focal distance and the parfocal position doesn't exist. Therefore an effective detection of the parfocality of the zoom lens sets will increase a productivity and a product quality of the stereo microscope.
Three problems should be solved in the detection of the parfocality of the zoom lens sets. The first problem is the judgment of definition, a relatively clearest position at present magnification can be obtained via a definition judging model; the second problem is the judgment of parfocality, whether the relatively clearest position at present magnification is the parfocal position can be judged via a parfocality judging model; the third problem is to fit a parfocality position curve at the continuous magnifications according to the parfocality positions detected under the discrete magnifications.
At present, an artificial observing method is adopted in the detection of the parfocality of the zoom lens sets. The artificial observing method comprises: adjusting the magnification of the stereo microscope to a maximum value firstly and adjusting the microscope to obtain a clear image; then decreasing the magnification, observing whether the image is clear, if the image is not clear, slightly adjusting the focal distance to obtain the clear image, and recording a clear position as the parfocal position; repeating the above steps to obtain a group of parfocal positions at different magnifications; and estimating the parfocal positions under the continuous magnifications by experience, according to the parfocal positions under the discrete magnifications, to further obtain an empirical curve. The artificial observing method is low in efficiency, and erroneous judgment easily happens to influence the product quality. On the other hand, when a product yield is increased and a full inspection of the product is required, a large number of detecting workers are required. Therefore the artificial observing method can only be applied in initial product trial-manufacturing stage, but in a mass production, a more efficient parfocality detecting method is required.